WO 2007/106339 A2 discloses a light application apparatus for applying light to the skin of a person for treating the skin, for example, for removing hair from the skin. In an embodiment, light from one or more light emitting diodes is used for treating the skin, wherein some of the light passes through the epidermis and, in particular, the dermis prior to being reflected back to a sensor. An electronic control system uses the output of the sensor to control the operation of the apparatus. This allows controlling the operation of the apparatus depending on a property of the skin.